The present invention relates to a radiation image photographing apparatus, and particularly relates to a radiation image photographing apparatus constituted so as to apply bias voltage to radiation detecting elements.
Various types of radiation image photographing apparatuses are developed, such as so-called direct type radiation image photographing apparatuses that generate charge by detecting elements in accordance with the dose of radiation, such as irradiated X rays and converts the charge into electric signals, and so-called indirect type radiation image photographing apparatus that converts irradiated radiation into electromagnetic waves with other wave length, such as visible light by scintillator and the like, then generates charge corresponding to the energy of the converted and irradiated electromagnetic waves by photoelectric converting elements, such as photo-diodes, and converts the charge into electric signals (i.e., image data).
These types of radiation image photographing apparatus are known as FPD (Flat Panel Detector). Conventionally, such the radiation image photographing apparatus are formed integrally with a support base (or bucky apparatus) (for example, refer to Patent Document 1). However, in recent years, the radiation detecting elements and the like are accommodated in a housing, so that portable type radiation image photographing apparatuses capable of being carried with portability are developed and put in practical use (for example, refer to Patent Documents 2 and 3).
In such radiation image photographing apparatuses, for example, as shows in FIG. 4 and FIG. 8 which are mentioned later, usually, radiation detecting elements 7 are disposed respectively in small regions divided by a plurality of scanning lines 5 and a plurality of signal lines 6 which are disposed to cross each other on a base plate 4, and a plurality of radiation detecting elements 7 is arranged in a two dimensional form (a matrix form) so that a detecting section P is formed.
Moreover, switch sections constituted with thin film transistors (hereafter, merely referred to as TFTs) 8 are connected to the respective radiation detecting elements 7, and further bias lines 9 to apply a bias voltage are connected to the respective radiation detecting elements 7. Moreover, the respective scanning lines 5 are connected to gate drivers 15b of a scan driving section 15, and the respective signal lines are connected to a read-out circuit 17 in a read-out IC 16.
At the time of radiation image photography, radiation is irradiated to the radiation image photographing apparatus on the condition that the respective TFTs 8 are turned to OFF state with the application of OFF voltage from the gate driver 15b to all of the scanning lines 5. Then, charges generated in the respective radiation detecting elements 7 upon irradiation with radiation are accumulated in the respective radiation detecting elements 7.
After the irradiation of radiation, when ON voltage is applied sequentially from the gate driver 15b to the respective scanning lines 5, the charges accumulated in the respective radiation detecting elements 7 are discharged to the signal lines 6 via the TFTs 8 turned to ON state, the charges are converted into electric signals, i.e., image data by the read-out circuit, and the image data are read out.
Patent document 1: Japanese Unexamined Patent Publication No. H9-73144 official report
Patent document 2: Japanese Unexamined Patent Publication No. 2006-058124 official report
Patent document 3: Japanese Unexamined Patent Publication No. H6-342099 official report
Incidentally, according to investigation by the present inventors, for example, as shown in FIG. 22A, when radiation is irradiated to a radiation image photographing apparatus 1 having the above-mentioned structure on the condition that the irradiation field is limited to a small region, on the portions other than the portion A irradiated with radiation, the values of the image data read out from the respective radiation detecting elements 7 are expected to become small uniformly.
However, it turns out that actually, there may be a case where, as shown in FIG. 22B, a phenomenon that the image data D of the portion B of the respective radiation detecting elements 7 connected to the same scanning line with the respective radiation detecting elements 7 on the portion A irradiated with radiation becomes smaller than the image data D of the respective radiation detecting elements 7 on the other portion C, i.e., a phenomenon that cross talk occurs in the elongated direction of the scanning lines 5 (that is, in the traverse direction in the figure, hereafter, referred to as the scanning line direction), may appear.
In this case, when image data D are checked in the arrowed mark direction (in this case, in the elongated direction of the signal lines 6) shown in FIG. 22B, for example, as shown in FIG. 23, the image data D of the portion B of the respective radiation detecting elements 7 connected to the same scanning line with the respective radiation detecting elements 7 on the portion A irradiated with radiation becomes smaller wholly than the image data D of the respective radiation detecting elements 7 on the other portion C.
Further, reversely, as shown in FIG. 24A, when a shielding plate is placed on a part of the radiation image photographing apparatus F and radiation being not so strong is irradiated uniformly all over the apparatus F, on the portions other than the portion α where the shielding plate was placed, the values of the image data D read out from the respective radiation detecting elements 7 are expected to be the uniform value. However, actually, there may be a case where, as shown in FIG. 24B, a phenomenon that the image data D of the portion β of the respective radiation detecting elements 7 connected to the same scanning lines with the respective radiation detecting elements 7 on the portion α where the shielding plate was placed, become larger than the image data D of the respective radiation detecting elements 7 on the other portions γ, (that is a phenomenon that cross talk occurs in the elongated direction of the scanning lines), may appear.
If such cross talk occurs, for example, in the case where diseased parts of a patient are photographed with the radiation image photographing apparatus F used in radiation image photography for medical service, cross talk as shown in FIG. 22B occurs in the scanning line direction on the portion (i.e., so-called “direct pass-through portions”) of the radiation image photographing apparatus F to where radiation is irradiated directly without passing through a body of a patient being an object to be photographed, or cross talk as shown in FIG. 24B occurs on the portion of the radiation image photographing apparatus F at where an amount of radiation having arrived to the radiation image photographing apparatus 1 is small due to absorption into the body or scattering by the body when radiation passes through the body of a patient.
Therefore, when a radiation image is produced based on the read-out image data, various influences of cross talk appear on the radiation image, so that the radiation image is not likely to be observed easily.
Accordingly, if influences of cross talk appear on the radiation image, there is fear that the portions of cross talk are erroneously observed as diseased parts, or diseased parts are overlooked due to difficulty in observation for the diseased parts under the influence of cross talk.